In many situations, especially involving military shelters, it is desirable to have a non-metallic housing and still provide protection against electro-magnetic interference signals. Aside from the individuals within the shelters, the shelters often enclose critical electronic equipment which would malfunction if subjected to electro-magnetic waves. Also, when certain types of electronic equipment are used, it is desirable to have shelters which avoid detection of the location from which the signals are generated. In these cases, protective shields may be placed within the walls of the shelters.
Heretofore, electro-magnetic protection has been provided by using solid aluminum skins on the inside surface of the shelter, sometimes sandwiched with a fibrous skin which forms the exterior of the shelter. The locations of aluminum skins inside of the walls of the shelters produce problems because of the likelihood that the aluminum may be penetrated accidentally or otherwise, as when inserts are attached to the aluminum.
Placing thin aluminum shields on the outside of the shelters subjects them to damage and defeats a primary purpose of a non-metallic shelter which is to provide a durable, damage and environmental resistant outer skin.
Any shield employed should be capable of providing full protection for the shelter, with no openings at the corners or areas where panels are joined to form the shelter.
Some U.S. patents relating to shielding include Nos. 2,405,987; 3,231,663; 3,231,451; 3,030,435 and 4,037,009.